Chevrolet Repair: El Camino brake question..., salvage yard, decent shape

Question
Van:
It's the damndest thing...
I've got a 1979 El Camino (350 engine) in pretty decent shape.  It sat for several years, and...while I know that's never good for a vehicle...it only has 75,000 miles.
Lately, when I add brake fluid and pop the little plastic top back on the master cylinder, a small leak appears right where the master cylinder is attached to the booster cylinder.  A small bead of brake fluid begins slowly trickling down the booster cylinder, sometimes even dripping onto the ground.
The drip doesn't start until I pop the little plastic top back on the master cylinder, so I guess there has to be a small amount of pressure on the fluid.  Also, the fluid level in the master cylinder never drains completely out, but stops about halfway below the "Full" line on the master cylinder's side.
Is there a gasket between the master cylinder and the booster cylinder that could be worn out or defective, allowing this small leak?
Any suggestions, advice greatly appreciated.
Warm regards,
David Gardner
davidg32@yahoo.com

Answer
Hello David,
Not so much a gasket, as a little rubber grommet type seal.
I think it only drains that far because the pressure depletes.
If you want to test that theory, when it quits leaking, remove the cap, and then, without adding fluid, replace the cap again, and see if it leaks some more.
You may need to buy the reservoir to get the seals, I'm not sure.
Might try a salvage yard.
Better yet, just replace the complete master cyl/reservoir. Good safe investment.

Van